Currently the lighting or signalling system: trailers, semi-trailers, is supplied by the general system of the tractor of the vehicle (tractor) through a male/female connecting plug, this connection is obligatory because only the tractor has the electric energy to permit operation both at night and day of the lighting devices used on the vehicle.
Usually, in the case of long waits, the signalling lights or position of the entire articulated truck (tractor with trailer) are switched off because if they were kept on and with the engine switched off the battery would run down in a short period of time, compromising the function of the vehicle; whereas in the case of a switched-on engine, fuel would be consumed and a contribution to the emission of environmental pollutants would be obtained unnecessarily.